This application is a competitive renewal of "A Squirrel Monkey Breeding and Research Resource" which has received continuous NCRR support since 1980. The overall goals of this project are to provide a national research resource of squirrel monkeys and their tissues and to carry out research leading to a better understanding of squirrel monkey biology and research uses. This project has evolved over the years into the only breeding resource of squirrel monkeys in the United States available to NIH grantees. This has led to the development of a research and management group with expertise on reproduction, diseases, and basic biology on the squirrel monkey. The project meets biomedical research needs in three ways. First, it provides a national resource of laboratory- born squirrel monkeys. Second, our research activities continue to add new information about the biology of squirrel monkeys with particular emphasis on reproductive biology and colony management. Third, the resource provides tissues and biological fluids to investigators throughout the country, thus reducing the need for additional living animals. The scarcity of squirrel monkeys for research and difficulties associated with captive breeding experienced by most laboratories emphasize the need to continue research into the reproductive biology, social behavior, veterinary medical care, and husbandry management of the genus. These areas of investigation have been integrated into a multi-disciplinary program designed to meet the needs of the breeding resource and investigators who use squirrel monkeys in their research. In this way, a self-sustaining supply of squirrel monkeys has been established for biomedical research use, and our understanding of the basic biology of squirrel monkeys continues to grow. Over the past 18 years, much of our research has focused on characterization of the natural reproductive processes and diseases of squirrel monkeys. This has led to improvements in reproductive performance. Proposed research activities will focus on continuing to expand our knowledge of reproduction of squirrel monkeys including the development of in vitro reproduction, embryo culture, embryo and gamate preservation, and pilot studies to determine the feasibility of creating a transgenic squirrel monkey. Investigation of natural biological processes will continue with studies of progesterone resistance and risk factors associated with reproductive loss. The proposed studies address important issues in biomedicine while increasing our understanding of squirrel monkey biology. This balance between scientific investigation and breeding resource management has created an environment that encourages inquiry and collaborative investigations while provide a scarce non-human primate research resource to other institutions and investigators.